Applied modifiers are not visible
Modifiers are automatic operations that affect an object’s geometry in a non-destructive way. With modifiers, you can perform many effects automatically that would otherwise be too tedious to do manually (such as subdivision surfaces) and without affecting the base geometry of your object.


They work by changing how an object is displayed and rendered, but not the geometry which you can edit directly. You can add several modifiers to a single object to form The Modifier Stack and Apply a modifier if you wish to make its changes permanent.



Apply (Ctrl+A)


Makes the modifier “real”: converts the object’s geometry to match the applied modifier’s results, and deletes the modifier.


Warning


Applying a modifier that is not first in the stack will ignore the stack order (it will be applied as if it was the first one), and may produce undesired results.

(From the Blender Manual)